The need for means to safely install wheels on tractor/trailer combination vehicles has long been recognized and numerous solutions have been made available. However, these solutions are limited in application because they are of a single nut design without the means to be rigidly fixed and secured in position on the axle spindle.
In 1965, a major producer of highway trailers introduced a new industry axle having a wheel retention system consisting of a single nut held in place by a cotter pin. At that time, there was no interest in providing an axle nut system which could be adjusted for specific amounts of preload; a compressive force on the bearings, because the tapered roller bearing manufacturers did not advocate advantages would occur with that type of installation. The technique of wheel installation with that trailer manufacturer's single nut design was merely to tighten the wheel assembly in place and then back off the single nut to a position of loose clearance before placing a cotter pin in position to prevent rotational movement. The disadvantages of this arrangement soon materialized with a rash of "lost wheels" resulting in many disastrous accidents. Investigations showing the single axle nut marketed by this trailer manufacturer were unsafe for a number of reasons and the following conclusion issued by the National Highway Traffic Safety Administration: "Analysis reveals that a problem did exist which (the company) should have addressed with a safety recall in 1984". For specifics regarding this issue, attention is invited to the NHTSA Engineering Analysis Action Report EA88-024, dated Jun. 5, 1989.
Subsequent to the publication of the National Transportation Safety Board Special Investigation Report, NTSB/SIR-92/04, PB92-917004, adopted Sep. 15, 1992, which detailed accounts of lost wheel incidents, recommendations were directed to the attention of the American Trucking Association specifying the need to "Promote an educational program on proper wheel tightening procedures through carriers, manufacturers, government".
Recognizing the need for remedial action, efforts were initiated leading to the development of this invention. Coupled with this recognition was the awareness of industry's progress to improve tapered roller bearing adjustment. With this stimulation, the Controlled Position Axle Nut System was conceived and tested with substantiating results.
Because a potential weakness with all single nut designs produced for the industry is the inability to consistently eliminate all degrees of freedom between the threads of the spindle and those of the nut, it was part of the initial parameters to develop a retention system configured with jamming members to control this problem. In the course of development, several tapered roller bearing manufacturers advised that a controlled amount of preload within the tapered roller bearings wheel assembly was not only acceptable, but it would be recommended if an accurate means could be achieved for that purpose.
Until the time of this invention, no double nut configuration was capable of being installed on the axles of tractor/trailer combination vehicles with the means of providing any measure of controlled preload on the tapered roller bearings. In achieving the final jammed condition between the two nuts involved, it was always the case that the outer nut had to be tightened against the inner nut and during that process additional pressure was brought to bear against the bearings. The amount of additional preload pressure was relative to the amount of thread clearance which existed between the threads of the inner nut and the threads of the spindle. The tolerances of manufactured threads on axle nuts were so variable that inconsistent preload pressures would occur as a result of the inward movement of the inner nut through the space or lash between mating threads as the outer nut was tightened into the jammed condition. For this reason, the recommended practices by all manufacturers for installation of double nuts on tractor/trailer applications call for a back off of the inner nut prior to installing and tightening the outer nut. Currently, at this writing, recommendations have not been published indicating that tapered bearing preload would be acceptable but this has been projected to occur in the near future.
With the availability of this double member jamming retention system; A Controlled Position Axle Nut System, it is now possible to apply a specific amount of preload and to retain that pressure on the bearings during the subsequent and final tightening operation. An additional advantage of this invention is its ability to install and maintain a specific amount of clearance between the bearing and the retention members if so desired.